A heat-developable light-sensitive material usually contains either a base or a base precursor for the purpose of accelerating development due to heating. From the viewpoint of the storage stability of the light-sensitive material, it is preferred to use the base precursor releasing a basic substance on thermal decomposition.
Typical examples of such base precursors are described in British Pat. No. 998,949. Preferred base precursors are the salts of carboxylic acids and organic bases; useful carboxylic acids include trichloroacetic acid and trifluoroacetic acid, and useful bases include guanidine, piperidine, morpholine, p-toluidine, and 2-picoline. Particularly useful is guanidine trichloroacetate described in U.S. Pat. No. 3,220,846. In addition, aldoneamides described in Japanese Patent Application (OPI) No. 22625/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") are preferably used since they produce bases upon decomposition at elevated temperatures.
Many of these base precursors, however, need relatively long periods of time for the formation of images and are likely to cause fogging. In addition, they have disadvantages in that they are readily influenced by air or moisture and thus are likely to undergo decomposition under the influence of air or moisture, thereby causing variations in the photographic properties of the light-sensitive material and deteriorating the storage stability of the light-sensitive material.